1. Field of the Invention
This invention relates to a blood treatment apparatus with an extracorporeal circuit, and more particularly to a blood treatment apparatus wth two membrane modules different in performance. It also relates to a method of treating blood.
2. Description of Prior Art
Various blood treatment techniques such as hemodialysis using a dialysis membrane, hemofiltration with a filtration membrane and hemoperfusion with an adsorbent, among others, have come into wide clinical use. Recently, a technique called plasmapheresis, which is one of the extracorporeal blood treatment techniques, has been developed. Said plasmapheresis comprises first separating blood into plasma and corpuscular components and then treating the plasma by a certain technique, thereby removing pathogenic factors. More specifically, plasmapheresis includes the plasma exchange method in which the plasma is exchanged for a plasma preparation and the specific plasma component permeation method which comprises further fractionating the plasma, removing the problematic fraction and returning the remaining fractions, together with the corpuscular components, to the circulation. When viewed as a therapeutic means, the plasma exchange method is not always preferable because the whole amount of the plasma should be exchanged. This requires a large amount of a plasma to be prepared at great expense. Also, when using the plasma exchange method, adverse effects may be produced due to incomplete supplementation of various physiologic substances contained in the plasma. On the contrary, the specific plasma component permeation method can be regarded as a more desirable therapeutic means, since only a part of the plasma is discarded while the rest is returned to the circulation, substantially overcoming the two problems mentioned above.
Pioneer studies of the specific plasma component permeation method have already been made and described. For example, there is a report by T. Agishi et al, published in the Japanese Journal of Medical Instrumentation, vol. 49, Supplement, p. 259-261 (1979). Also, a Japanese patent application laid open under No. 2444/1980 discloses a blood treatment apparatus in which a specific plasma component permeation method is realized in combination with a water-removing means.
However, these techniques known in the art, though called techniques, are no more than proposals of possibilities or theoretical apparatus. No invention can be found therein for an apparatus useful in medical practice.